PORT-AU-PRINCE, Haiti – Hunger turned to anger in Haiti's capital on Wednesday as hundreds of protesters marched through the streets accusing local officials of demanding bribes for donated food.

Aid workers say that food and other supplies are now flowing into the country three weeks after the Jan. 12 quake, but red tape, fear of ambush, transportation bottlenecks and corruption are keeping it from many people who need it.

Hungry protesters jogged along a broad avenue in the Port-au-Prince suburb of Petionville waving branches and chanting, "They stole the rice! They stole the rice!"

One of the protesters, 17-year-old Danka Tanzil, said a local official was demanding a bribe in return for coupons that entitle people to bags of donated food from the U.N. World Food Program. "For us to get the coupon, we must give 50 Haitian dollars (US$7) so we can get the rice," she complained.

People at small protests elsewhere had a simpler message, holding up banners reading, in English: "Help us, We're starving."

The World Food Program began distributing the coupons to bring order to the aid distribution and prevent strong young men from forcing themselves to the front of food lines. Aid officials say it has largely worked, despite scattered reports of abuses.

The U.N. agency "is aware of reports that our coupons have been resold, and we've also heard allegations of forgeries," WFP spokeswoman Jennifer Parmelee said. "However, all evidence from our cooperating partners who are managing the distributions ... is that this is not a widespread issue."

The agency said it has reached more than 300,000 people through the coupon program but needs to reach 2 million.

In other key developments:

• U.N. Secretary-General Ban Ki-Moon asked former U.S. President Bill Clinton to expand his role as special envoy for Haiti by taking a stronger role in coordinating relief and reconstruction efforts.

• Haiti's Ministry of Health, backed by the U.N. and other agencies, began a campaign to give vaccinations against key diseases to 250,000 children under age 7 living in temporary settlements. It said 200,000 other injured people will get tetanus vaccines.

• Senegal's President Abdoulaye Wade told Radio France International that dozens of Haitians have asked about taking advantage of his offer of free land for Haitians who want to "return to their origins" in Africa following the earthquake.

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Associated Press Writers Martha Mendoza and John Rice in Mexico City and Todd Pittman in Dakar, Senegal, contributed to this report.